1. Field of the Invention
The invention relates to a power converting device, more particularly to a bidirectional DC-to-DC power converting device.
2. Description of the Related Art
FIG. 1 illustrates a conventional bidirectional power converting device disclosed in U.S. Pat. No. 7,382,113. The conventional bidirectional power converting device is coupled between a rechargeable battery 21 and a capacitor 22, and is operable so that an input voltage is supplied by one of the rechargeable battery 21 and the capacitor 22 is converted into an output voltage that is to be supplied to the other one of the rechargeable battery 21 and the capacitor 22. When the input voltage, i.e., VL, is supplied by the rechargeable battery 21 for conversion into the output voltage, i.e., VH, that is to be supplied to the capacitor 22 for charging the capacitor 22, the rechargeable battery 21 serves as a power source and the capacitor 22 serves as a load. On the other hand, when the input voltage, i.e., VH, is supplied by the capacitor 22 for conversion into the output voltage, i.e., VL, that is to be supplied to the rechargeable battery 21 for charging the rechargeable battery 21, the capacitor 22 serves as a power source and the rechargeable battery 21 serves as a load.
The conventional bidirectional power converting device includes a coupling circuit 1, a first switch 101, a second switch 102, a third switch 103, a first diode 111, a second diode 112, a third diode 113, a first capacitor 121, a second capacitor 122, and an inductor 13. The coupling circuit 1 includes first and second windings 11, 12 each having a polarity end and a non-polarity end. The polarity end of the first winding 11 is coupled to the rechargeable battery 21. The non-polarity end of the first winding 11 is coupled to the polarity end of the second winding 12. The first switch 101 is coupled between the non-polarity end of the first winding 11 and ground, and is operable between an ON-state and an OFF-state. The first diode 111 has an anode coupled to the non-polarity end of the first winding 11, and a cathode. The first capacitor 121 is coupled between the cathode of the first diode 111 and ground. The third diode 113 has an anode coupled to the cathode of the first diode 111, and a cathode. The second capacitor 122 is coupled between the non-polarity end of the second winding 12 and the cathode of the third diode 113. The second diode 112 has a grounded anode and a cathode. The inductor 13 is coupled to the polarity end of the first winding 11 and the cathode of the second diode 112. The second switch 102 is coupled between the cathodes of the second and third diodes 112, 113. The third switch 103 is coupled between the cathode of the third diode 113 and the capacitor 22. Since the operation of the conventional bidirectional power converting device is described in detail in the aforesaid patent, further discussion of the same is omitted herein for the sake of brevity.
It is noted that the inductor 13 and the diodes 111, 112, 113 are utilized to achieve bidirectional power conversion. However, since the diodes 111, 112, 113 have conduction losses larger than those of the switches 101, 102, 103, and since soft switching characteristics of the switches 101, 102, 103 are unapparent, the conventional bidirectional power converting device has inferior power transformation efficiency. Moreover, due to the presence of the inductor 13, the conventional bidirectional power converting device has a relatively large volume and incurs relatively high costs.